| From Nov.2009 to Sep.2010,197 female specimens of Megalobrama pellegrini were collected for studies of ovary development and oogenesis from Longxi River (Shidong and Texing reach in Luzhou), which is a main branch of Yangtze River.The histology and transmission electron microscop were used for observation of the morphological and structure changes with ovary development and oogenesis. PAS, SBB and other histochemistry methods were used for observation of the morphology and distribution of glucid, fat and protein in oogenesis. Protein, fat and other chemical components of ovary in different stages were measured by Kjeldahl method, Saxhlet extraction and other methods. The results were as follows:Based on size, shape and external color, the development of ovary in Megalobrama pellegrini was divided into six stages. Ovary in stageâ… was transparent, we could distinguish male and female only by histotomy and staining. In stageâ…¡, the ovary was fresh red, flat-ribbon and some capillaries can be seen. As for the stageâ…¢, it was flat-cystiform and pale yellow, granulous oocytes gleamed in ovary. As for the stageâ…£, it was round-cysticform and deep yellow, granulous oocytes and numerous blood vessels can be seen obviously. In the stageâ…¤, it was baggy-cysticform and eggs would be flowing out when the abdomen was pressed. Ovary of stageVIwas stage after oviposition, it was empty-cysticform and congestive, only few oocytes in degradation could be seen in ovary.According to changes of inner structures, yolk accumulating and development of follicle cells, the oogenesis of Megalobrama pellegrini could be divided into six phases. The first phase was phase of oogonium, oogoniums were clustering distribution and mainly consisted in ovary of stageâ… . Second, was phase of oocytes with single-layer follicle cells, which mainly consisted in stageâ…¡. Ovary wall formed and grew up in this phase, follicle cell formed and grew up from sporadic to single-layer. Yolk nucleus appeared in the cytoplasm, the number of nucleolus increased and nucleolus vacuoles were formed in this phase. Third, was phase of oocyte with yolk vesicles, which mainly consisted in stageâ…¢. Yolk vesicle appeared and grew up from outer of cytoplasm to inner, loop of growth appeared in the cytoplasm and yolk vesicles began to accumulate yolk. Follicle cells differentiated into double-layer cells and oolemma differentiated zona radiata and microvilli in this phase. The fourth phase was phase of oocyte filled with yolk, which mainly consisted in stage IV, accumulating of yolk mainly happened in this phase. It had three layers of follicle cells and zona radiata becomed thicker. Cortical alveoli appeared and loop of membranous was obviously existented in cytoplasm, yolk granule and numbers of cortical alveoli increased with development of oocyte. The fifth phase was phase of mature oocyte, which mainly consisted in stageâ…¤, cytoplasm of oocyte was filled with yolk granules, nuclear membranes disappeared and follicle cells were separated from oocyte. The sixth phase was phase of oocyte in degeneration, which consisted in stageâ…¥, yolk liquefied and absorbed by follicle cells.By means of transmission electron microscope, oogonium was round with a big central nucleolus, there were a lot of ribosomes and mitochondriums in the cytoplasm. In phase of pre-vitellogenesis, the number of nucleolus increased, with lower electronic densify nucleolus vesicals in the nucleolus. Mitochondria cloud was formed by clustering mitochondria, then mitochondrium moved to outer of cytoplasm. In phase of early-vitellogenesis, follicle cells differentiated and formed digitations, these digitations and digitations formed by oocyte crossed and formed microvilli. Zona radiata 1 was formed in inner edge of oolemma and yolk vesicle was formed in outer edge of cytoplasm, high electronic densify could be seen in yolk vesicle. In phase of late-vitellogenesis, microvilli becomed thicker and zona radiatathe 2 and 3 formed which were inner Zl.Kinds of organelles including mitochondrium and endoplasmic reticulum and ribosome were activated to vitellogenesis, yolk granules began to fusing and formed yolk plate. In phase of mature oocyte, follicle cells degenerated and oocyte was filled with yolk plate.Histochemical studies gave the following results:glucide mainly distributed in yolk vesicle, microvilli, zone radiata, yolk granule, loop of membranous, cortical alveoli, yolk plate. Fat mainly distributed in loop of growth, zone radiata, cortical alveoli, loop of membranous, yolk granule, yolk plate. Protein mainly distributed in zone radiata, microvilli, loop of growth, cortical alveoli, loop of membranous, yolk granule, yolk plate. Loop of growth and loop of membranous of oocyte in Megalobrama pellegrini might be complex, which contained fat, glucide and protein. Loop of membranous might be formed by moving of loop of growth or deposition of yolk granule. We found three forms yolk in vitellogenesis:yolk vesicle, yolk granule and cortical alveoli, they were complex which contained fat, glucide and protein, there were only yolk plate in mature oocytes.With ovary development in Megalobrama pellegrini, weight of ovary increased from 0.1g to 44.7g, GSH was changed from 0.1% to 17.53%. Water content of ovary was highest and reducing progressively with ovary development. Protein content and carbohydrate content increased progressively. Ash content and fat content were first increased and later reduced, then increased slowly. Increment analysis of these five components showed:increment of water was largest, second was increment of proein, then was increment of carbohydrate, increment of ash and fat was small. Increment of these five compositions focused on stage ofâ…¢-â…¤, which agreed with results of our histochemical study. |
PDF Full Text Request